Police should not use stun guns on people who try to evade custody but pose no safety risk to the officers or others, a federal appeals court decided in a ruling that will affect law enforcement procedures in five states.

The 4th U.S. Circuit Court of Appeals waded into an evolving legal field this week when it ruled in the case of a mentally ill man in North Carolina.

A three-judge panel said Ronald H. Armstrong, clinging tightly to a sign post to avoid being taken to a hospital, was no threat to anyone when he was shot five times with a Taser by Pinehurst police. Minutes later, Armstrong was dead.

The appeals court said the officers used excessive force, but they could not have been expected to know they were going too far because of a patchwork of conflicting legal decisions on similar cases across the country. Because of the muddled legal landscape, the officers were entitled to “qualified immunity” that barred Armstrong’s estate from collecting damages, the court said.

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In the future, however, the court made it clear that officers facing circumstances similar to those in Armstrong’s case must keep their stun guns holstered.

“While qualified immunity shields the officers in this case from liability, law enforcement officers should now be on notice that such Taser use violates the Fourth Amendment,” Judge Stephanie D. Thacker wrote.

The Richmond-based appeals court’s decisions are binding in South Carolina, North Carolina, West Virginia, Maryland and Virginia.

The ruling, published Monday, has caused a ripple effect across the law enforcement community in those states.

The decision prompted an advisory on Friday to all law enforcement agencies in South Carolina from the director of the state police training academy.

“It is important that you immediately contact your legal counsel to discuss this case and amend your policy,” wrote S.C. Criminal Justice Academy director Hubert Harrell. Each police agency – not the academy – determines its own training program, academy spokeswoman Florence McCants said Saturday.

Harrell’s advisory underscored an excerpt from the court’s ruling. “(Tasers), therefore, may only be deployed when a police officer is confronted with an exigency that creates an immediate safety risk and that is reasonably likely to be cured by using the taser.”

The North Carolina Justice Academy said in a memo to law enforcement agencies that the opinion “dramatically changes the legal landscape” governing stun gun use. It advised police departments to revise their written policies and comply with the ruling, and said officers should be ready to defend any use of force against a noncompliant subject.

Dana Schrad, executive director of the Virginia Association of Chiefs of Police, said she plans to notify members about the ruling.

“Clearly this will be something that, if it stands, will have an impact on a lot of police procedures,” she said.

She said if officers are reluctant to use their stun guns, they may resort to other physical means more likely to cause injuries.

“Or they will step back and not intervene at all,” which would not be in anyone’s best interests, she said.

Karonnie R. Truzy, attorney for Armstrong’s estate, said he was disappointed with the immunity ruling but gratified that the case established a clear rule for police.

“This solidifies what everyone in the public thinks should be happening: When you are unarmed and no threat, you should not be subject to force,” Truzy said.

The Associated Press and Staff Writer Clif LeBlanc contributed to this article.